Nitrogen-, oxygen- and sulfur-containing PACs are among the bacterial mutagens which are known to be produced within a wide range of combustion devices. The formation and destruction of these species will be studied in turbulent diffusion flames of natural gas, liquid fuel and pulverized coal using the combustion tunnel of the MIT Combustion Research Facility (CRF). The experiments permit detailed characterization of in flame measurements and sampling under well controlled combustion conditions of generic industrial flame types. Recent studies at the MIT-CRF have shown that nitrogen containing PACs form preferentially from products of fuel pyrolysis and NOX. This observation raises the question whether fuel-rich/fuel-lean sequencing, the preferred method of NOX emission control in practical flames, is conducive to the formation of such direct acting mutagens. Major objectives of the proposed study are to identify the nitrogen-, oxygen- and sulfur-containing PACs in the flame, their contribution to the biological activity of flame samples, and to determine the combustion conditions under which they are formed. Such information will not only be directly applicable to combustion in devices of industrial scale, but it will also be valuable in indicating the measures appropriate to reducing emissions from smaller-scale equipment which has greater propensity for unhealthful emissions when operated in a hot-cold cyclic manner. The detailed flame structure measurements will permit the interpretation of the flame data in terms of local rates of formation and destruction of the highly mutagenic PACs and provide the basis for combustion process modification aimed at their selective reduction.